U.S. patent application number 11/639397 was filed with the patent office on 2008-06-19 for emissions conformance for an exhaust after-treatment system having a dosing agent supply.
Invention is credited to Sherif H. El Tahry, John A. Pinson, Michael A. Potter, Fabien G. Redon, Christopher C. Wright.
Application Number | 20080141659 11/639397 |
Document ID | / |
Family ID | 39432053 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141659 |
Kind Code |
A1 |
Potter; Michael A. ; et
al. |
June 19, 2008 |
Emissions conformance for an exhaust after-treatment system having
a dosing agent supply
Abstract
An exhaust after-treatment system for a vehicle including a
dosing agent that is selectively injected into an exhaust from a
dosing agent supply includes a first module that determines a level
of a dosing agent source. A second module selectively impedes
vehicle operation by adjusting an engine operating mode if the
level of said dosing agent source is below a threshold level.
Inventors: |
Potter; Michael A.; (Grass
Lake, MI) ; Redon; Fabien G.; (Southfield, MI)
; El Tahry; Sherif H.; (Troy, MI) ; Wright;
Christopher C.; (Howell, MI) ; Pinson; John A.;
(Troy, MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21, P O BOX 300
DETROIT
MI
48265-3000
US
|
Family ID: |
39432053 |
Appl. No.: |
11/639397 |
Filed: |
December 14, 2006 |
Current U.S.
Class: |
60/285 |
Current CPC
Class: |
Y02T 10/40 20130101;
F02D 2200/0802 20130101; F01N 2610/03 20130101; F01N 2610/1406
20130101; Y02T 10/26 20130101; Y02A 50/20 20180101; F02D 41/024
20130101; Y02T 10/47 20130101; F02D 41/3035 20130101; F01N 3/021
20130101; F02B 3/06 20130101; Y02A 50/2322 20180101; F01N 11/00
20130101; F02D 2041/227 20130101; F02B 1/12 20130101; F01N 13/009
20140601; F01N 3/36 20130101; Y02T 10/12 20130101; F01N 2250/02
20130101; F02D 41/22 20130101; F02D 41/0002 20130101 |
Class at
Publication: |
60/285 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Claims
1. An exhaust after-treatment system for a vehicle including a
dosing agent that is selectively injected into an exhaust from a
dosing agent supply, comprising: a first module that determines a
level of a dosing agent source; and a second module that
selectively impedes vehicle operation by adjusting an engine
operating mode if said level of said dosing agent source is below a
threshold level.
2. The exhaust after-treatment system of claim 1 wherein said
vehicle operation is impeded by one of reducing a fueling rate to
an engine of said vehicle, limiting an operating speed of said
engine, limiting an operating speed of said vehicle, limiting an
acceleration rate of said vehicle and altering a combustion mode of
said engine.
3. The exhaust after-treatment system of claim 2 wherein said
fueling rate is determined based on said level of said dosing agent
source.
4. The exhaust after-treatment system of claim 2 wherein said
threshold level corresponds to a low condition of said dosing agent
source, and said fueling rate and a dosing rate are regulated to
achieve a desired emissions performance.
5. The exhaust after-treatment system of claim 2 wherein said
combustion mode is altered to be a pre-mixed charge compression
ignition (PCCI) combustion mode.
6. The exhaust after-treatment system of claim 1 wherein said
threshold level corresponds to an empty dosing agent source, and
one of reducing a fueling rate to an engine of said vehicle,
limiting an operating speed of said engine, limiting an operating
speed of said vehicle, limiting and acceleration rate of said
vehicle and altering a combustion mode of said engine is performed
to achieve a desired emissions performance.
7. The exhaust after-treatment system of claim 1 wherein said
vehicle operation is impeded by rendering said vehicle unable to
drive.
8. The exhaust after-treatment system of claim 1 wherein said
second module discontinues inhibiting vehicle operation when said
dosing agent source is replenished to raise said level above said
threshold level.
9. A method of extending emissions performance of an exhaust
after-treatment system of a vehicle that includes a dosing agent,
comprising: determining a level of a dosing agent source; and
selectively impeding vehicle operation by adjusting an engine
operating mode if said level of said dosing agent source is below a
threshold level.
10. The method of claim 9 wherein said vehicle operation is impeded
by one of reducing a fueling rate to an engine of said vehicle,
limiting an operating speed of said engine, limiting an operating
speed of said vehicle, limiting and acceleration rate of said
vehicle and altering a combustion mode of said engine.
11. The method of claim 10 further comprising determining said
fueling rate based on said level of said dosing agent source.
12. The method of claim 10 wherein said threshold level corresponds
to a low condition of said dosing agent source, and further
comprising regulating said fueling rate and a dosing rate to
achieve a desired emissions performance.
13. The method of claim 10 wherein said combustion mode is altered
to be a pre-mixed charge compression ignition (PCCI) combustion
mode.
14. The method of claim 9 wherein said threshold level corresponds
to an empty dosing agent source, and further comprising performing
one of reducing a fueling rate to an engine of said vehicle, and
altering a combustion mode of said engine to achieve a desired
emissions performance.
15. The method of claim 9 wherein said vehicle operation is impeded
by rendering said vehicle unable to drive.
16. The method of claim 9 further comprising discontinuing
inhibiting vehicle operation when said dosing agent source is
replenished to raise said level above said threshold level.
17. A method of extending emissions performance of an exhaust
after-treatment system of a vehicle that includes a dosing agent,
comprising: determining a level of a dosing agent source;
determining whether a vehicle is at a convenient location; and
selectively impeding vehicle operation by adjusting an engine
operating mode if said level of said dosing agent source is below a
threshold level and said vehicle is not at said convenient
location.
18. The method of claim 17 wherein said vehicle operation is
impeded by one of reducing a fueling rate to an engine of said
vehicle, limiting an operating speed of said engine, limiting an
operating speed of said vehicle, limiting and acceleration rate of
said vehicle and altering a combustion mode of said engine.
19. The method of claim 18 further comprising determining said
fueling rate based on said level of said dosing agent source.
20. The method of claim 18 wherein said threshold level corresponds
to a low condition of said dosing agent source, and further
comprising regulating said fueling rate and a dosing rate to
achieve a desired emissions performance.
21. The method of claim 18 wherein said combustion mode is altered
to be a pre-mixed charge compression ignition (PCCI) combustion
mode.
22. The method of claim 17 wherein said threshold level corresponds
to an empty dosing agent source, and further comprising performing
one of reducing a fueling rate to an engine of said vehicle,
limiting an operating speed of said engine, limiting an operating
speed of said vehicle, limiting and acceleration rate of said
vehicle and altering a combustion mode of said engine to achieve a
desired emissions performance.
23. The method of claim 17 wherein said vehicle operation is
impeded by rendering said vehicle unable to drive.
24. The method of claim 17 further comprising discontinuing
inhibiting vehicle operation when said dosing agent source is
replenished to raise said level above said threshold level.
25. The method of claim 17 further comprising disabling operation
of said vehicle if said level of said dosing agent source is below
said threshold level and said vehicle is at said convenient
location.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. Ser. No. (To Be
Assigned), filed on Dec. 14, 2006 (GP-307049), entitled, "Method of
Monitoring A Dosing Agent Supply For Treating Exhaust", and U.S.
Ser. No. (To Be Assigned), filed on Dec. 14, 2006
(GP-308227-PTE-CD), entitled, "Diesel Exhaust Control During
Limp-Home Mode". The disclosures of the above applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to vehicle exhaust systems,
and more particularly to a method of extending emissions
performance under a reduced or depleted exhaust treatment system
dosing agent supply.
BACKGROUND OF THE INVENTION
[0003] Internal combustion engines combust an air and fuel mixture
to generate drive torque. The combustion process generates exhaust
that is exhausted from the engine to atmosphere. The exhaust
contains nitrogen oxides (NOx), carbon dioxide (CO.sub.2) and
carbon monoxide (CO) and particulates. An exhaust after-treatment
system treats the exhaust to reduce regulated emissions prior to
being released to atmosphere.
[0004] In an exemplary exhaust after-treatment system, a dosing
system injects a dosing agent (e.g., urea) into the exhaust
upstream of a catalyst. The exhaust and dosing agent mixture reacts
over the catalyst to reduce the level of emissions. The dosing
system includes a dosing agent supply and an injector. The amount
of dosing agent injected is based on the level of emissions in the
exhaust. If the dosing agent supply is empty or at a low level,
insufficient dosing agent is injected into the exhaust stream and
emissions are not reduced as desired.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention provides an exhaust
after-treatment system for a vehicle including a dosing agent that
is selectively injected into an exhaust from a dosing agent supply.
The system includes a first module that determines a level of a
dosing agent source, and a second module that selectively impedes
vehicle operation by adjusting an engine operating mode if the
level of said dosing agent source is below a threshold level.
[0006] In other features, the vehicle operation is impeded by at
least one of reducing a fueling rate to an engine of the vehicle,
limiting the operating speed of the engine, limiting the operating
speed of the vehicle, limiting the acceleration ability of the
vehicle and altering a combustion mode of the engine. The fueling
rate is determined based on the level of the dosing agent source.
In one embodiment, the threshold level corresponds to a low
condition of the dosing agent source, and the fueling rate and a
dosing rate are regulated to achieve a desired emissions
performance. In another embodiment, the vehicle speed is regulated
to achieve a desired emission performance. In another embodiment,
the combustion mode is altered to be a pre-mixed charge compression
ignition (PCCI) combustion mode. In still another embodiment, these
actions are combined to achieve the desired emission
performance.
[0007] In another feature, the threshold level corresponds to an
empty dosing agent source, and at least one of reducing a fueling
rate to an engine of the vehicle, limiting the operating speed of
the engine, limiting the operating speed of the vehicle, limiting
the acceleration ability of the vehicle and altering a combustion
mode of the engine is performed to achieve a desired emissions
performance.
[0008] In still another feature, the vehicle operation is impeded
by rendering the vehicle unable to drive.
[0009] In yet another feature, the second module discontinues
inhibiting vehicle operation when the dosing agent source is
replenished to raise the level above the threshold level.
[0010] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the
description and specific examples are intended for purposes of
illustration only and are not intended to limit the scope of the
present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0012] FIG. 1 is a functional block diagram of an exemplary vehicle
system including an exhaust after-treatment system according to the
present invention;
[0013] FIG. 2 is a flowchart illustrating exemplary steps executed
by the extended emissions conformance control of the present
invention;
[0014] FIG. 3 is a flowchart illustrating exemplary steps executed
by extended emissions conformance control to determine whether the
vehicle system is stopped at a convenient location; and
[0015] FIG. 4 is a functional block diagram illustrating exemplary
modules that execute the extended emissions conformance
control.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The following description of the preferred embodiment is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses. For purposes of clarity, the
same reference numbers will be used in the drawings to identify
similar elements. As used herein, the term module refers to an
application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that
execute one or more software or firmware programs, a combinational
logic circuit, or other suitable components that provide the
described functionality.
[0017] Referring now to FIG. 1, an exemplary vehicle system 10 is
schematically illustrated. The vehicle system 10 includes an engine
system 12, an exhaust after-treatment system 14. The engine system
12 includes an engine 16 having a cylinder 18, an intake manifold
20 and an exhaust manifold 22. Air flows into the intake manifold
20 through a throttle 24. The air is mixed with fuel and the air
and fuel mixture is combusted within the cylinder 18 to drive a
piston (not shown). Although a single cylinder 18 is illustrated,
it is appreciated that the engine 12 may include additional
cylinders 18. For example, engines having 2, 3, 4, 5, 6, 8, 10, 12
and 16 cylinders are anticipated. Furthermore, although a throttle
is illustrated, the present disclosure can be implemented in engine
systems that do not include a throttle. The fuel is provided from a
fuel source 26 and is mixed with air to form a combustion mixture.
A fuel level sensor 30 is responsive to the amount of fuel within
the fuel source 26.
[0018] Exhaust is produced through the combustion process and is
exhausted from the cylinder 18 into the exhaust manifold 22. The
exhaust after-treatment system 14 treats the exhaust flowing
therethrough to reduce emissions before being released to the
atmosphere. The exhaust after-treatment system 14 includes a dosing
system 32, a diesel oxidation catalyst (DOC) 34, an emissions
sensor 36 and a catalyst 38 that is preferably provided as a
selective catalytic (SCR) catalyst. The DOC 34 reacts with the
exhaust to reduce emission levels of the exhaust. The emissions
sensor 36 is responsive to an emissions
[0019] (e.g., NOx) level of the exhaust. It is also anticipated
that a diesel particulate filter (DPF) 40 may be located downstream
from the catalyst 30 that filters diesel particulates to further
reduce emissions.
[0020] The dosing system 32 includes a dosing agent injector 42, a
dosing agent storage tank 44 and a dosing agent supply sensor 46.
The dosing system 32 selectively injects a dosing agent (e.g.,
urea) into the exhaust stream to further reduce emissions. More
specifically, the amount of the dosing agent is determined based on
the signal generated by the exhaust sensor, which can alternatively
be provided as a virtual sensor (i.e., a model based function that
omits the physical sensor). The dosing agent decomposes in the
exhaust and the resulting constituents react within the catalyst 38
to further reduce exhaust emissions.
[0021] A control module 50 regulates operation of the vehicle
system 10 based on the extended emissions conformance control of
the present invention. More specifically, the control module 50
determines a dosing agent level (DA.sub.LEVEL) based on the signal
generated by the dosing agent supply sensor 46. The control module
can calculate a vehicle range (RANGE.sub.DA) based on the amount of
dosing agent remaining. More specifically, RANGE.sub.DA indicates
the remaining drivable distance before the entire dosing agent is
consumed. RANGE.sub.DA can be displayed on a display (not shown) to
alert the vehicle operator.
[0022] If DA.sub.LEVEL is below a first predetermined or low dosing
agent threshold value (DA.sub.LOW), the control module 50 sets a
low dosing agent flag (FLAG.sub.DALOW) (e.g., equal to 1 or TRUE)
indicating that the dosing agent level is low and should be
refilled. Additionally, the control module 50 activates an
indicator 52 that alerts the vehicle operator that the dosing agent
supply is low and should be refilled. The indicator 52 can be a
visual and/or audible indication that alerts the vehicle operator
to the low condition. If DA.sub.LEVEL is below a second
predetermined or empty dosing agent threshold value (DA.sub.EMPTY),
the control module 50 sets an empty dosing agent flag
(FLAG.sub.DAEMPTY) (e.g., equal to 1 or TRUE). Further, the control
module 50 activates the indicator 52 to indicate that the dosing
agent source 44 is empty. When the dosing agent source 44 is
refilled and DA.sub.LEVEL exceeds DA.sub.EMPTY and/or DA.sub.LOW,
FLAGDAEMPTY and/or FLAG.sub.DALOW is/are cleared and the indicator
52 is also cleared.
[0023] The extended emissions conformance control selectively
impedes vehicle operation based on the dosing agent level. More
specifically, if the dosing agent monitoring control determines
that the vehicle is at a convenient location, a convenient location
flag (FLAG.sub.CL) is set (e.g., equal to 1 or TRUE). A convenient
location can include, but is not limited to, a fuel station, a
maintenance workshop and/or an oil change workshop. If
FLAG.sub.DALOW is set and the vehicle is stopped at a convenient
location (i.e., a location where additional dosing agent is
available) the extended emissions conformance control disables
operation of the vehicle by setting a disable flag (FLAG.sub.DIS)
until the dosing agent is replenished. It is also anticipated,
however, that the vehicle operation need not be disabled even
though the vehicle is at a convenient location, but can be impeded,
as described in further detail below.
[0024] The extended emissions conformance control selectively
impedes operation of the vehicle. One case includes when
FLAG.sub.DAEMPTY is set and FLAG.sub.CL is not set (i.e., when the
vehicle is not deemed to be at a convenient location). Vehicle
operation is impeded by relaxing the drivability and fuel economy
constraints, and employing more aggressive modes of combustion that
reduce emissions. In one embodiment, a combustion strategy, such
as, for example, pre-mixed charge compression ignition (PCCI)
combustion can be used. PCCI combustion is known to significantly
reduce NO.sub.X and particulate emissions, however, may decrease
fuel economy and increase engine noise. In an alternative
embodiment, fueling levels are reduced. By lowering the fueling
levels, engine power levels, NO.sub.X and particulate emissions are
correspondingly reduced. In a further embodiment, the vehicle speed
and/or acceleration ability (i.e., limiting the achievable rate of
acceleration) of the vehicle is limited. By employing one of, or a
combination of these strategies, the extended emissions conformance
control enables the desired emissions performance to be achieved
even though the dosing agent is depleted. As a result, an emissions
compliant limp-home mode is provided without the need to disable
the vehicle.
[0025] In an alternative embodiment, the extended emissions
conformance control impedes vehicle operation when FLAG.sub.DALOW
is set. In this manner, although the remaining dosing agent can be
utilized in hand with the above-described engine operating modes,
to maximize emissions performance, while extending the dosing agent
range. For example, the fueling levels can be reduced based on
DA.sub.LEVEL to reduce emissions, and at the same time, the
remaining dosing agent can be used to further reduce emissions
below the desired level. By combining fueling level reduction and
dosing agent emissions reduction, the drivability and fuel economy
are not as adversely affected as would be by reducing fueling
levels alone to achieve the desired emissions performance.
[0026] Referring now to FIG. 2, exemplary steps executed by the
extended emissions conformance control will be described in detail.
In step 200, control determines FLAG.sub.CL. In step 202, control
monitors DA.sub.LEVEL. Control calculates and displays RANGE.sub.DA
in step 204 based on DA.sub.LEVEL. In step 206, control determines
whether DA.sub.LEVEL is less than DA.sub.LOW. If DA.sub.LEVEL is
not less than DA.sub.LOW, control clears all dosing agent related
flags in step 208 and control ends. If DA.sub.LEVEL is less than
DA.sub.LOW, control determines whether DA.sub.LEVEL is less than
DA.sub.EMPTY in step 210. If DA.sub.LEVEL is not less than
DA.sub.EMPTY, control sets FLAG.sub.DALOW in step 212 and control
continues in step 213. If DA.sub.LEVEL is less than DA.sub.EMPTY,
control sets FLAG.sub.DAEMPTY in step 216 and control continues in
step 218.
[0027] In step 218, control determines whether FLAG.sub.CL is set.
If FLAG.sub.CL is not set, control continues in step 213. If
FLAG.sub.CL is set, control sets FLAG.sub.DIS in step 220. Control
disables vehicle operation in step 222 and continues in step 213.
In step 213, control impedes vehicle operation by implementing one
of or a combination of the strategies discussed in detail above. In
step 214, control displays the dosing agent status based on the
dosing agent related flags and control ends. For example, "Dosing
Agent Low", "Dosing Agent Empty" or "Vehicle Disable Due To Empty
Dosing Agent" messages can be displayed.
[0028] Referring now to FIG. 3, exemplary steps executed by the
extended emissions conformance control to determine whether the
vehicle is stopped at a convenient location will be described in
detail. In step 300, control determines whether an engine start
just occurred. If an engine start occurred, control continues in
step 302. If an engine start did not occur, control continues in
step 304.
[0029] In step 302, control determines FUEL.sub.LEVEL. In step 306,
control determines .DELTA.FUEL.sub.LEVEL as the difference between
FUEL.sub.LEVEL and the fuel level that was stored in memory
immediately prior to the last engine shut-off event. In step 308,
control determines whether .DELTA.FUEL.sub.LEVEL is greater than a
threshold difference (.DELTA..sub.THR). If .DELTA.FUEL.sub.LEVEL is
greater than .DELTA..sub.THR, control determines that the vehicle
was refueled during the most recent shut-down and continues in step
310. If .DELTA.FUEL.sub.LEVEL is not greater than .DELTA..sub.THR,
control determines that the vehicle was not refueled during the
most recent shut-down and continues in step 312.
[0030] In step 304, control continuously monitors FUEL.sub.LEVEL.
In step 314, control determines whether FUEL.sub.LEVEL is
increasing at a rate (e.g., dFL/dt) greater than a threshold rate
(e.g., dFL/dt.sub.THR). If dFL/dt is greater than dFL/dt.sub.THR,
control determines that the vehicle is being refueled and continues
in step 310. If dFL/dt is not greater than dFL/dt.sub.THR, control
determines that the vehicle is not being refueled and continues in
step 312. In step 310, control sets FLAG.sub.CL. In step 312,
control stores the new or most recent FUEL.sub.LEVEL into memory
and control ends.
[0031] Although the extended emissions conformance control is
described in detail above using the fueling station scenario as an
example, it is appreciated that the extended emissions conformance
control can monitor other scenarios including, but not limited to,
maintenance and/or oil change to determine whether the vehicle is
located in a convenient location. For example, the extended
emissions conformance control can monitor vehicle maintenance flags
stored in memory and determine that the vehicle is at a convenient
location if one or more maintenance related flags are set or reset.
Alternatively, the extended emissions conformance control can
monitor an oil level or an oil characteristic. For example, if the
oil level (OIL.sup.LEVEL) increases or an oil parameter
(OIL.sub.PAR) (e.g., including, but not limited to, electrical
impedance) indicates that an oil change has just occurred, the
extended emissions conformance control can determine that the
vehicle is at a convenient location to refill the dosing agent.
[0032] Referring now to FIG. 4, exemplary modules that execute the
extended emissions conformance control of the present invention
will be described in detail. The exemplary modules include a
FLAG.sub.DALOW module 400, a FLAG.sub.EMPTY module 402, a
RANGE.sub.DA module 404, a FLAG.sub.CL module 406, a display module
408, an AND module 410, an indicator module 412, a disable module
414 and an impede module 416. The FLAG.sub.DALOW module 400, the
FLAG.sub.EMPTY module 402 and the RANGE.sub.DA module 404 can be
individual modules or can be sub-modules within a larger module
418.
[0033] The FLAG.sub.DALOW module 400 selectively sets
FLAG.sub.DALOW based on DA.sub.LEVEL and DA.sub.LOW. Similarly, the
FLAG.sub.DAEMPTY module 402 selectively sets FLAG.sub.DAEMPTY based
on DA.sub.LEVEL and DA.sub.EMPTY. The RANGE.sub.DA module 404
calculates RANGE.sub.DA based on DA.sub.LEVEL. The FLAG.sub.CL
module 406 selectively sets FLAG.sub.CL based on FUEL.sub.LEVEL,
OIL.sub.LEVEL and/or OIL.sub.PAR. It is also anticipated that
FLAG.sub.CL can be selectively set based on maintenance flags or
any other factor that would indicate the vehicle is at a convenient
location. The display module 408 graphically displays RANGE.sub.DA
to alert the vehicle operator to the remaining distance the vehicle
can travel before the dosing agent source is empty or below a
desired level.
[0034] The AND module 410 generates a signal based on
FLAG.sub.DAEMPTY and FLAG.sub.CL. For example, if both
FLAG.sub.DAEMPTY and FLAG.sub.CL are set (e.g., equal to 1) the AND
module 410 outputs a signal indicating that the dosing agent is
empty and the vehicle is located at a convenient location. The
indicator module 412 generates an indication signal (e.g., audible
and/or visual) based on FLAG.sub.DAEMPTY or FLAG.sub.DALOW to alert
the vehicle operator to the status of the dosing agent source. The
disable module 414 selectively disables vehicle operation based on
the output of the AND module 410. More specifically, the disable
module 414 generates control signals that disable vehicle operation
until the dosing agent source is replenished. The impede module 416
selectively impedes vehicle operation based on FLAG.sub.DAEMPTY,
the output of the AND module 410, FLAG.sub.DALOW and/or
DA.sub.LEVEL. More specifically, the impede module 416 implements
one of or a combination of the strategies described in detail
above, and generates corresponding control signals.
[0035] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings, the
specification and the following claims.
* * * * *